The present invention relates to medical stents and related methods. More specifically, the invention relates to medical stents having one section which is softer than a section at the other end of the stent.
Fluid sometimes needs to be drained from a body. For example, urine formed in one or both kidneys might need to be drained into the bladder. One way to accomplish such drainage is to use a medical device that conveys the fluid (e.g., urine) through a lumen. Such devices include stents and catheters. Existing stents can be uncomfortable for the patient, especially when they reside in the ureter between the kidney and the bladder, can be difficult for a medical professional to place in a patient, or can allow urine from the bladder to move into the ureter towards the kidney.
The present invention provides medical stents for facilitating drainage of fluid and methods for placing such stents. For example, such stents can be placed in a ureter to facilitate drainage of fluid from a patient""s kidney to a patient""s bladder. Generally, stents according to the invention have a xe2x80x9csofterxe2x80x9d end and a xe2x80x9charderxe2x80x9d end. The harder end generally resides in the patient""s kidney while the softer end generally resides in the patient""s bladder. The harder end can transition to the softer end in a transition section produced by, for example, a co-extrusion process where deposition of a first material is gradually ceased and deposition of a second is gradually increased. In general, the harder end is suited to retain the stent in the patient""s kidney and/or facilitate placement in a patient, while the softer end is suited to increase patient comfort and/or retain the stent in the patient""s bladder. Additionally, the softer end can inhibit movement of the stent in the bladder, minimize contact between the stent and the bladder, at least partially occlude the junction between the bladder and ureter in order to at least partially prevent retrograde urine flow from the bladder into the ureter both around the stent and through the stent, and/or otherwise minimize reflux of urine through the stent towards the kidney. Such stents also are useful in other situations such as biliary drainage or, generally, where fluid is drained from one body structure to another body structure or out of the body.
In one embodiment, a medical stent can include a first section defining a lumen and including a first coil completing more than one revolution, a second section defining a lumen and including a second coil completing at least one revolution, and a third section defining a lumen and located between the first and second sections. The first section can include a first material having a first durometer value, and the second section can include a second material having a second durometer value. The second durometer value can be greater than the first durometer value, and at least a portion of the third section can include a co-extrusion of the first and second materials. The first coil can revolve about and be coaxial with an axis. A distance from a first point to the axis, the first point being at the center of a first cross-section of the first coil and on a line normal to the axis, can be less than a distance from a second point to the axis, the second point being at the center of a second cross-section of the first coil and on a line normal to the axis and the first point being closer to an origin of the first coil than the second point. The third section can be adjacent the origin of the first coil.
The embodiment described above, or those described below, can have any of the following features. The axis can generally extend along the third section. The second coil can be offset from the axis. The third section can include a shaft. The second coil can be generally perpendicular to the first coil. The first material can be ethylene vinyl acetate. The first material can have a durometer value of about 70 to about 90 on a Shore A scale. The second material can have a durometer value of about 80 to about 95 on a Shore A scale. A cross-section of the lumen in at least one of the first, second, and third sections can be circular. A cross-section of at least one of the first, second, and third sections can be circular. At least one of the first, second, and third section can include a radiopaque material. The second coil can have an outer diameter of at least about 2.0 cm. The first coil can be sized and/or shaped such that at least a portion of the first coil resides at the junction of a bladder and a ureter in a patient. The first coil can be a spiral.
In another aspect of the invention, a medical stent can include a first section defining a lumen and including a substantially planar first coil completing more than one revolution, a second section defining a lumen and comprising a second coil completing at least one revolution, and a third section defining a lumen and located between the first and second sections. The first section can include a first material having a first durometer value, and the second section can include a second material having a second durometer value. The second durometer value can be greater than the first durometer value. At least a portion of the third section can include a coextrusion of the first and second materials. The second coil can be generally perpendicular to the first coil.
In another aspect of the invention, a method for placing a medical stent includes inserting a medial stent, including any of the stents described above or below with any of the features described above or below, into a ureter. At least a portion of the first coil can reside at the junction of a bladder and a ureter in a patient. At least a portion of the first coil can at least partially occlude the junction.